The present invention generally relates to the fabrication of staircases, particularly to staircases which are at least partially curved, and, in a representatively illustrated embodiment thereof, more particularly relates to improved construction techniques for such staircases.
Conventional factory fabrication of a curved staircase, for subsequent shipment to an installation site, is typically initiated by the laborious construction of a horizontally spaced pair of temporary vertical support walls with curvatures conforming to the curved paths which the opposite sides of the completed staircase will ultimately assume. The opposite sides of the staircase, in the form of elongated “stringer” structures, are then secured along their lengths to these support walls in the predetermined curving and rising paths of the staircase sides.
The staircase stringers are typically of a laminated wooden construction formed by elongated thin wooden laminae which are glued together in the usual horizontally side-to-side orientation. In forming each stringer it is customary to secure one or more initial layers thereto to its associated support wall and then secured and glue successive layers to the previously secured layer(s) until the stringer is laterally built up to its necessary thickness.
After the stringers have been formed in place in this manner on the support walls, careful measurements are made and riser/tread notches are hand-cut into upper side edges of the stringers for later receipt of the riser and tread portions of the individual step structures which will extend across the stringers. It is necessary that these riser/tread notches be cut into the stringers after the stringers are laterally built up to their full widths. It is exceedingly difficult, if not impossible, to pre-cut the riser/tread notches in the individual stringer laminae and then have them properly align with their adjacent laminae notches in the subsequently built-up stringers.
Next, careful measurements are taken on and between the completed stringers for the purpose of fabricating the individual riser and tread member portions of the staircase. When these staircase components are subsequently fabricated, they are operatively positioned on and secured to the temporary wall-supported stringers. Finally, the partially completed staircase is carefully removed from the temporary support walls for pre-finishing and shipment to the job side where attachment of the remaining staircase components (such as the hand rail and balusters) and installation of the completed staircase carried out.
Even from the brief description above, it can readily be seen that the conventional fabrication of a curved staircase is fraught with tedium, complexity, expense and a variety of potential constructional inaccuracies. For example, great care and considerable amount of construction are typically required to accurately erect the temporary support walls onto which the stringer and step portions of the staircase are initially built. Additionally, a similar amount of care is required to correctly lay out the curved, rising stringer paths on these walls so that the completed stringers are accurately configured with respect to both their rises and their curvatures. Further, because the built-up stringers ultimately determined the precise shapes and dimensions of the risers and treads, a great deal of hand forming, matching and fitting is required to fabricate these staircase elements and operatively secure them to the stringers.
After all of this is done, of course, the task still remains to remove the completed staircase portion from its associated support walls and ready the finished staircase structure for shipment. Because a curved staircase of this type is often a one-of-a kind custom design, the laboriously constructed support walls are, in most instances, simply torn apart since that layout is of no further use except in constructing that particular staircase or one essentially identical thereto.
Additionally, because the stringer structures must be bent around the temporary support walls (around either their inner or outer side surfaces) and firmly secured thereto, the outer side surfaces of the stringers, which would normally define the “finished” outer side surfaces of the completed staircase, are frequently marred or otherwise damaged. This typically necessitates the securement to the stringers of a sheet of finishing veneer material after their removal from the temporary support walls, thereby further adding to the overall labor time and expenses associated with the staircase.
The complexity and precision entailed in this conventional staircase fabrication technique renders it, as a general proposition, unsuitable for on-site use by a general construction contractor. Accordingly, it is normally carried out only in a factory setting by skilled woodworking artisans.
Many of these problems, limitations and disadvantages were at least substantially reduced by the improved curved staircase manufacturing methods illustrated and described in the present applicant's U.S. Pat. Nos. 5,163,491 and 5,347,774. In a first staircase construction method disclosed in these patents, preformed step structures have treads with curved slots formed in the underside of their ends which define a path for insertion of top edge segments of thin starter strips. The slots are collectively configured to laterally deflect the inserted starter strips in a manner longitudinally conforming them to at least partially curved paths of the overall stringer structures in the completed staircase. The stringers are then laterally built up and completed by securing reinforcing structures to the side surfaces of the laterally deflected strips.
A second staircase construction method disclosed in these patents used preformed cooperating treads and risers themselves as a form which defines an at least partially curved path for the stringers. Simple temporary supports both position the cooperating treads and risers and provide a solid support for laying up strips from the inside out to form stringers to support the stair and back finishing strips along curved paths defined by the cooperating treads and risers wherein the finishing strips have edges configured to interengage the outer ends of the cooperating treads in a rigid assembly and for smooth sides of the staircase.
While these staircase construction methods provide needed improvements to the above-described conventional method of utilizing complex temporary wall structures to form an at least partially curved staircase structure which is shipped to the job side in an assembled state, they still present various problems, limitations and disadvantages. For example, a considerable amount of skill and time is required to accurately assemble the staircase at the job site and to properly fabricate the laminated stringer portion, layer-by-layer, along the entire length of the staircase. Additionally, since the joints between the adjacent pairs of stringer laminae are essentially vertical in the assembled staircase, vertical loads on the staircase undesirably impose vertical shear loading on the stringer structures. This can cause unsightly buckling and separation of the stringer laminae which may be quite difficult to repair.
From the foregoing it can be seen that it would be desirable to provide further improved staircase manufacturing methods and resulting staircase apparatus for shipment to a job site for final fabrication and installation. It is to this goal that the present invention is primarily directed.